The bottom line is the guy has to understand the burden of proof that he is doing correct lies with him. Tell him, not to sit there and explain to some chic at the PO that its a gun. Just ship it. Worst that will happen is the postmaster will find it, then contact the aTF, and by ATF rules, its legal to ship from person to person, muzzleloading rifles, and antique (replicas also) from person to person.